Pandemic potential Bird flu viruses are just a few genetic steps away from the flu virus that caused the deadly 1918 Spanish flu pandemic, a new study shows.

An international team of virologists identified the key genetic components — similar to those in the virus behind the 1918 pandemic — in influenza viruses in wild ducks.

The findings, published in the journal Cell Host and Microbe , suggest that 1918-like pandemic viruses may emerge in the future.

"Because avian influenza viruses in nature require only a few changes to adapt to humans and cause a pandemic, it is important to understand the mechanisms involved in adaptations … so we can be better prepared," says study lead author Yoshihiro Kawaoka of the University of Wisconsin-Madison.

The Spanish flu killed up to 50 million people across the world in 1918.

Previous genetic analysis indicates the deadly virus was a type of influenza A of avian origin, although this finding is controversial.

Wild birds harbour a large gene pool of influenza A viruses that could cause pandemics, but the likelihood of birds harbouring a virus similar to the 1918 pandemic virus has been unclear.

To assess the risk, the scientists used reverse genetic methods to recreate a virus that differed from that of the Spanish flu by only 3 per cent of the amino acids that make the virus proteins.

In the animals it was tested on, the new virus was less pathogenic than the Spanish flu — but more so than avian flu.

However, the scientists then discovered seven mutations in three virus genes that allowed it to spread as easily as the Spanish flu in ferrets, an animal commonly used in influenza transmission studies.

Consisting of genetic factors already present in wild bird populations, the virus showed that genetic ingredients capable of combining to create a dangerous pathogen that could produce a human pandemic exist in nature.

Surveillance strategies

Kawaoka says the discovery could help scientists develop more effective strategies to combat the emergence of such a disease.

"Research findings like this help us assess the risk of outbreaks and could contribute to routine surveillance of influenza viruses," he says.

The research also shines light on the bird flu virus's adaptive mechanisms for spreading to mammals.

A mutation of a protein on the surface of the virus, for example, allows it to cling to an organism's cells and could increase the virus's ability to infect human respiratory tracts.

The researchers also discovered that the virus they created reacted to the current vaccine against seasonal flu — which is effective against H1N1 flu responsible for a 2009 pandemic — indicating that the current vaccine could offer protection against a pandemic.

The scientists also noted that the virus was sensitive to oseltamivir, an antiviral medication to prevent and slow the flu.